Memory devices based on electric field programmable films

ABSTRACT

A composition for the formation of an electric field programmable film, the composition comprising a matrix precursor composition or a dielectric matrix material, wherein the dielectric matrix material comprises an organic polymer and/or a inorganic oxide; and an electron donor and an electron acceptor of a type and in an amount effective to provide electric field programming. The films are of utility in data storage devices.

CROSS-REFERENCE OF RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/500,082 filed Sep. 3, 2003, the entire contents of which are herebyincorporated by reference.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Grant No.F49620-01-1-0427 awarded by AFOSR.

BACKGROUND

The present disclosure relates to electronic memory devices based onelectric field programmable films. More particularly, the presentdisclosure relates to electronic memory devices that exhibit bistablebehavior.

Electronic memory and switching devices are presently made frominorganic materials such as crystalline silicon. Although these deviceshave been technically and commercially successful, they have a number ofdrawbacks, including complex architecture and high fabrication costs. Inthe case of volatile semiconductor memory devices, the circuitry mustconstantly be supplied with a current in order to maintain the storedinformation. This results in heating and high power consumption.Non-volatile semiconductor devices avoid this problem but have reduceddata storage capability as a result of higher complexity in the circuitdesign, which results in higher production costs.

Alternative electronic memory and switching devices employ a bistableelement that can be converted between a high impedance state and a lowimpedance state by applying an electrical voltage or other type of inputto the device. Both organic and inorganic thin-film semiconductormaterials can be used in electronic memory and switching devices, forexample in thin films of amorphous chalcogenide semiconductor organiccharge-transfer complexes such ascopper-7,7,8,8-tetracyanoquinodimethane (Cu-TCNQ) thin films, and incertain inorganic oxides in organic matrices. These materials have beenproposed as potential candidates for nonvolatile memories.

A number of different architectures have been implemented for electronicmemory and switching devices based on semiconducting materials. Thesearchitectures reflect a tendency towards specialization with regard todifferent tasks. For example, matrix addressing of memory location in asingle plane such as a thin film is a simple and effective way ofachieving a large number of accessible memory locations while utilizinga reasonable number of lines for electrical addressing. Thus, for asquare grid having n lines in two given directions, the number of memorylocations is n². This principle has been implemented in a number ofsolid-state semiconductor memories. In such systems, each memorylocation has a dedicated electronic circuit that communicates to theoutside. Such communication is accomplished via the memory location,which is determined by the intersection of any two of the n lines. Thisintersection is generally referred to as a grid intersection point andmay have a volatile or non-volatile memory element. The gridintersection point can further comprise an isolation device such as anisolation diode to enable addressing with reduced cross-talk between andamong targeted and non targeted memory locations. Such grid intersectionpoints have been detailed by G. Moore, Electronics, Sep. 28, (1970), p.56.

Several volatile and nonvolatile memory elements have been implementedat the grid intersection points using various bistable materials.However, many currently known bistable films are inhomogeneous,multilayered composite structures fabricated by evaporative methods,which are expensive and can be difficult to control. In addition, thesebistable films do not afford the opportunity for fabricating films intopographies ranging from conformal to planar. Bistable films fabricatedusing polymer matrices and particulate matter are generallyinhomogeneous and therefore unsuitable for fabricating submicron andnanometer-scale electronic memory and switching devices. Still otherbistable films can be controllably manufactured by standard industrialmethods, but their operation requires high temperature melting andannealing at the grid intersection points. Such films generally sufferfrom thermal management problems, have high power consumptionrequirements, and afford only a small degree of differentiation betweenthe “conductive” and “nonconductive” states. Furthermore, because suchfilms operate at high temperatures, it is difficult to design stackeddevice structures that allow high density memory storage.

Accordingly, there remains a need in the art for improved electric fieldprogrammable bistable films that are useful as subsystems in electronicmemory and switching devices, wherein such films can be applied to avariety of substrates and produced with a variety of definabletopographies. Further, there is a need for electronic memory andswitching devices comprising electric field programmable bistable filmsthat can be produced more easily and inexpensively than known devices,that offer more useful differentiation between low conductivity and highconductivity states, that have reduced power and thermal requirementsand that can be stacked in various configurations to fabricateelectronic devices of higher density.

SUMMARY

In one aspect, a composition for the formation of an electric fieldprogrammable film, the composition comprising a matrix precursorcomposition or a dielectric matrix material, wherein the dielectricmatrix material comprises an organic polymer and/or a inorganic oxide;and an electron donor and an electron acceptor of a type and in anamount effective to provide electric field programming.

In another aspect, an electric field programmable film comprises adielectric matrix material, wherein the dielectric matrix materialcomprises an organic polymer and/or a inorganic oxide; an electrondonor; and an electron acceptor.

In another aspect, a method for manufacturing an electric fieldprogrammable film comprising applying the composition of claim 1 to asubstrate; and removing the solvent from the applied composition to forma film.

The present invention offers the advantages of simplicity ofmanufacture, higher device density and reduced cost of production. Theelectric field programmable film may be used in cross point array datastorage devices, stacked data storage devices, and the like. Inaddition, the electric field programmable film may be used in deviceshaving flexible plastic substrates, inorganic oxide substrates, opticaldevices, in switching elements for light emitting diodes, in switchingelements of other electronic devices such as sensors, as actuationelements in micro-electro-mechanical systems (MEMS) devices and incontrol applications in microfluidic devices.

DESCRIPTION OF THE DRAWINGS

FIG. 1( a) shows a schematic of an electric field programmable film;

FIG. 1( b) shows another schematic of an electric field programmablefilm;

FIG. 2( a) shows a cutaway view of a cross-point array data storagedevice with a continuous electric field programmable film;

FIG. 2( b) shows a cutaway view of a cross-point array data storagedevice with a plurality of pixilated electric field programmable filmelements;

FIG. 3( a) shows a schematic diagram of a cross point array devicecomprising electric field programmable film elements;

FIG. 3( b) shows a schematic diagram of a cross point array devicecomprising electric field programmable film elements;

FIG. 4 shows a cutaway partially exploded view of a stacked data storagedevice on a substrate;

FIG. 5 shows a cutaway partially exploded view of a stacked data storagedevice on a substrate;

FIG. 6 is shows a partially exploded cutaway view of another stackeddata storage device comprising a substrate and three device layers;

FIG. 7 provides, in a cutaway, contiguous, 7(a), and exploded, 7(b),views of a portion of a data storage device in which the memory elementsare isolated by junction diodes; and

FIG. 8 is a graphical representation of current vs. applied voltage forthe device of FIG. 1( b).

DETAILED DESCRIPTION

The electric field programmable film as defined herein is a filmcomprising active elements wherein the active elements are convertiblefrom a first electrically conductive or polarized state to a secondelectrically conductive or polarized state by the application of asuitable forward bias voltage, and wherein the material is re-convertedto its first electrically conductive or polarized state by theapplication of a suitable reverse bias voltage.

A forward bias voltage is an electrical signal applied to a device thatpromotes a change in a prescribed direction after the application of thebias voltage. A reverse bias voltage is the opposite of a forward biasvoltage of the same magnitude.

The active element is also called the electric field programmable filmelement and as defined herein is an intersection between an electrodefrom a first set of electrodes and an electrode from a second set ofelectrodes that can be altered by the application of a first stimulussuch that (a) the measured response is nonlinear or (b) the applicationof a subsequent, possibly different stimulus produces a differentmeasured response than the application of the first stimulus.

A cross-point array is a device comprising a first set of substantiallyparallel electrodes (also referred to as lines) running along a firstdirection, a second set of substantially parallel electrodes runningalong a second direction, wherein an active element is formed withinsome or all of the spatial intersections between an electrode from thefirst set of electrodes and an electrode from the second set ofelectrodes and further wherein the first direction is at an angle of 1to 179 degrees to the second direction and wherein the active elementcan be either continuous or pixelated.

Electric coupling as defined herein is that wherein a voltage or othersignal on one electrode relative to a reference or ground signal on asecond electrode can probe or change the state of the active element.Electrical coupling can be done via direct contact, or through anelectrical coupling element which makes ohmic contact, contact via aconducting plug, capacitive contact, contact via an intervening tunneljunction, contact via an intervening isolation device such as a diode ora transistor or contact via other electrical devices.

FIG. 1( a) shows a schematic of an electric field programmable film, 1,with a dielectric matrix material, electron donors (D), electronacceptors (A) and the optional donor acceptor complexes (DA). Theelectron donors (D), electron acceptors (A) and the optional donoracceptor complexes (DA) are also referred to as active components andrespond to the application of a stimulus. Examples of such stimuli mayinclude, but are not limited to, chemical, mechanical, electrical,magnetic, electromagnetic, electromechanical, magnetomechanical orelectrochemical. An exemplary stimulus is an electrical stimulus.

The dielectric matrix material is the carrier material for one or moreactive components in an active element. The dielectric matrix materialmay or may not itself comprise an active component. Matrix materialsutilized in the electric field programmable film composition aregenerally organic polymers or inorganic oxides. It is generallydesirable for the dielectric matrix material to form hydrogen bonds withthe electron donors and the electron acceptors. The hydrogen bondinglowers the free energy of the electric field programmable film whilehaving very little effect on the energy of the transition state forelectron transfer. Dielectric matrix materials that displaydipole-dipole interactions or dipole-induced dipole interactions mayalso be used in the electric field programmable film. The dielectricmatrix materials used in the electric field programmable films areorganic polymers and/or inorganic oxides.

It is desirable for the organic polymers used as the matrix materials tohave dielectric constants of 2 to 1000. In one embodiment, the organicpolymer has sufficient chemical and thermal resistance to withstandprocesses involving the deposition of metals, etch barrier layers, seedlayers, metal precursors, photoresists and antireflective coatings. Itis also desirable for the organic polymer to impart a low level ofelectrical conductivity to the electric field programmable film in the“off” state and to permit for a sufficiently high concentration ofelectron donors and electron acceptors to enable a sufficiently highconductivity in the “on” state so that the difference between the “off”state and the “on” state is readily discerned. Electrical conductivityof the dielectric matrix materials is less than or equal to about 10⁻¹²ohm⁻¹cm⁻¹. It is desirable for the ratio of the electrical current inthe “on” state to that in the “off” state to be greater than or equal to5, with greater than or equal to 100 being exemplary, and greater thanor equal to 500 being even more exemplary.

An on/off ratio greater than 5 allows the “on” and “off” states of anelectric field programmable film to be discerned readily while an on/offratio greater than 100 allows the “on” and “off” states to be discernedmore readily and anon/off ratio greater than 500 allows the “on” and“off” states to be discerned most readily. On/off ratios are engineeredto meet the requirements of the device. For example, devices having highimpedance sense amplifiers and requiring higher speed operation requirelarger on/off ratios, while in devices having lower speed requirementssmaller on/off ratios are acceptable.

The organic polymers that may be used as matrix materials in theelectric field programmable composition may be thermoplastics,thermosets, or blends of thermoplastics with thermosets. The organicpolymers may be homopolymers, block copolymers, graft copolymers, starblock copolymers, random copolymers, ionomers, dendrimers, or the like,or combinations comprising at least one of the foregoing organicpolymers.

Organic polymers having dielectric constant of 2 to 1,000 can be used.The dielectric constant (denoted by κ) of the matrix material can beselected such that “on” and “off” switching voltages are engineered toconform to the specific requirements of the application. Within theaforementioned range, organic polymers having dielectric constants ofgreater than or equal to about 4 are exemplary, with greater than orequal to about 6 being more exemplary, and greater than or equal toabout 7 being even more exemplary. Also desirable within this range is adielectric constant of less than or equal to about 450, with less thanor equal to about 400 being exemplary, and less than or equal to about350 being more exemplary.

Examples of suitable organic polymers that may be used as the dielectricmatrix materials in the electric field programmable film compositioninclude, but are not limited to polyolefins, poly(meth)acrylates,polyesters, polyamides, novolacs, polysiloxanes, polycarbonates,polyimides, polyacetates, polyalkyds, polyamideimides, polyarylates,polyurethanes, polyarylsulfone, polyethersulfone, polyphenylene sulfide,polyvinyl chloride, polysulfone, polyetherimide,polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidenefluoride, polyvinyl fluoride, polyetherketone, polyether etherketone,polyether ketone ketone, or combinations comprising at least one of theforegoing polymeric matrix materials.

Examples of suitable copolymers that may be used as the dielectricmatrix material in the electric field programmable composition filminclude, but are not limited to copolyestercarbonates, acrylonitrilebutadiene styrene, styrene acrylonitrile, polyimide-polysiloxane,polyester-polyetherimide, polymethylmethacrylate-polysiloxane,polyurethane-polysiloxane, or the like, or combinations comprising atleast one of the foregoing copolymers.

Examples of suitable thermosetting polymers that may be used in theelectric field programmable composition include, but are not limited topolyurethanes, natural rubber, synthetic rubber, epoxy, phenolic,polyesters, polyamides, silicones, or the like, or combinationscomprising at least one of the foregoing thermosetting polymers.

In an exemplary embodiment, the organic polymer in the electric fieldprogrammable film composition may be in the form of a matrix precursorcomposition comprising monomers. In one embodiment, the matrix precursorcomposition may be polymerized into a homopolymer or copolymer prior tothe casting of the electric field programmable film. In anotherembodiment, the matrix precursor composition may be polymerized into ahomopolymer or a copolymer after the composition is cast onto asubstrate to form the electric field programmable film.

Examples of suitable copolymers that may that may be used as matrixmaterials in the electric field programmable composition includecopolymers made from monomers selected from styrene, hydroxystyrene,C₁-C₁₀ linear, branched or cyclic alkyl, C₁-C₁₀ linear, branched, orcyclic alkoxy, C₆-C₁₀ aryl, arylalkyl, aryloxy or arylalkyloxysubstituted styrene, vinyl alcohol, vinyl acetate, (meth)acrylonitrile,(meth)acrylic acid, C₁-C₁₀ linear, branched, or cyclic alkyl, C₆-C₁₀aryl or arylalkyl (meth)acrylate esters, C₁-C₁₀ cyanoacrylate monomers,or the like, or a combination comprising at least one of the foregoingmonomers.

Polyester copolymers comprising C₁-C₁₀ linear, branched, or cyclicalkoxy; C₁-C₁₀ aryl, arylalkyl, aryloxy or arylalkyloxy dialcohols;C₁-C₁₀ linear, branched, cyclic alkoxy, C₁-C₁₀ aryl, arylalkyl, aryloxyor arylalkyloxy diacids may also be used in the electric fieldprogrammable composition. Polyamides comprising C₁-C₁₀ linear, branched,or cyclic alkoxy, C₁-C₁₀ aryl, arylalkyl, aryloxy or arylalkyloxydiamines; C₁-C₁₀ linear, branched, or cyclic alkoxy, C₆-C₁₀ aryl,arylalkyl, aryloxy or arylalkyloxy diacids may also be used in theelectric field programmable composition.

The organic polymers or copolymers may have a number average molecularweight (M_(n)) of about 50 to about 1,000,000 grams/mole (g/mole).Within this range, molecular weights of for example greater than orequal to about 100, greater than or equal to about 500, and greater thanor equal to about 1,000 g/mole may be used. Also desirable within thisrange are molecular weights of, for example, less than or equal to about750,000, less than or equal to about 500,000, and less than or equal toabout 250,000 g/mole.

As stated above, the dielectric matrix materials can be inorganicoxides. Exemplary inorganic oxides are those having a perovskitestructure characterized as having a tetravalent or trivalent atomsituated in an octahedral site with respect to the surrounding oxygenatoms. These materials have the general formulaA_(w)B^(x)C_(y)O_(z)where w, x, and y are 0 to 30, and z is 1 to 60; A is calcium,strontium, or barium, B is bismuth, zirconium, nickel or lead, and C istitanium, niobium zirconium vanadium, or tantalum. In an exemplaryembodiment, the stoichiometry is constrained to give approximate chargeneutrality.

When such inorganic oxides are used, the electron donors, electronacceptors and, optionally the donor-acceptor complexes must be capableof withstanding cure temperatures exceeding 200° C. Examples of suchinorganic oxides include, but are not limited to, lead zirconatetitanate (PZT), ferroelectric metal and mixed inorganic oxides withdielectric constants in amounts of 9 to 5500 such as barium strontiumtitanate (BST), lead lanthanum zirconate titanate (PLZT), bismuthstrontium tantalite, bismuth strontium niobate lead nickel niobate, leadmagnesium niobate and the like. It should be understood that the lattergeneric compound names are indicative of a range of stoichiometries. Forexample, bismuth strontium tantalite can have stoichiometries such asBi₂SrTa₂O₉, BiSr₂Ta₂O₉, Bi₂SrTa₂O₈ and so on. Inorganic oxides includetantalum oxide, niobium oxide, vanadium oxide, hafnium oxide, zirconiumoxide, titanium oxide, dysprosium oxide, yttrium oxide or the like orcombinations comprising at least one of the foregoing. The inorganicoxides offer a wide range of dielectric constants in amounts of 8 to1470.

Inorganic oxides may be converted into electric field programmable filmsvia sol-gel and chemical vapor deposition (CVD) techniques. When sol-geltechniques are used to from the electric field programmable film,electron donors, electron acceptors and, optionally the donor-acceptorcomplexes can be co-deposited.

Electron donors and acceptors can be dispersed randomly within thematrix material or agglomerated such that electronic conduction results,at least in part from percolative transport. An electron donor is amoiety capable of donating an electron to an electron acceptor. Anelectron acceptor is a moiety capable of accepting an electron from anelectron donor. The proposed mechanism for device can be betterunderstood with respect to the following reaction schemes shown in Table1:

TABLE 1 Scheme Reaction Event 1

Low conductivitystate. Kineticallystable because ofhigh barriertoelectron transport. 2

High conductivity“on” stateprogrammed. 3

High conductivitystate inthermodynamical-ly stableequilibrium. 4

HighConductivitystate. Mobileelectrons movefrom ionizedtonon-ionizedacceptors in thegeneral directionof the anode. 5

HighConductivitystate. Mobile“holes” movefrom ionizedtonon-ionizeddonors in thegeneral directionof the cathode. 6

Low conductivity“off” stateprogrammed.

In the schemes in Table 1, D and A represent electron donors andelectron acceptors, respectively. D⁺ and A⁻ represent a donor moietyhaving lost an electron and an acceptor moiety having gained anelectron, respectively. With reference to Table 1, a suprathresholdvoltage in forward bias drives the device from a low conductivity “off”state to a high conductivity “on” state; a subthreshold voltage inforward bias causes the device to exhibit a high conductivity in the“on” state and a low conductivity in the “off” state; a subthresholdvoltage in reverse bias causes the device to exhibit a high conductivityin the “on” state and a low conductivity in the “off state; and asuprathreshold voltage in reverse bias drives the device from a highconductivity “on” state to a low conductivity “off” state. Devicescapable of assuming either of two stable states, for example, a highconductivity state and a low conductivity state are generally calledbistable devices. In one example, forward bias voltages for convertingdevices having electric field programmable films from the low currentstate to the high current state are 0.1 to 15 V. In another example,voltages of 0.1 to 10 V are used. In one example, reverse bias voltagesfor converting devices having field programmable films from the highcurrent state to the low current state are −0.1 to −15 V. In anotherexample, voltages of −0.1 to −10 V are used.

Electron donors may be organic electron donors or inorganic electrondonors. Examples of organic electron donors include, but are not limitedto tetrathiafulvalene, 4,4′,5-trimethyltetrathiafulvalene,bis(ethylenedithio)tetrathiafulvalene, p-phenylenediamine,N-ethylcarbazole, tetrathiotetracene, hexamethylbenzene,tetramethyltetraselenofulvalene, hexamethylenetetraselenofulvalene, orthe like, or combinations comprising at least one of the foregoing.

The organic electron donors are 1 to 100 nanometers (nm) in size and areprevented from aggregating by protective organic or inorganic shells.Within this range, it is generally desirable to have organic electrondonors greater than or equal to 2, greater than or equal to 3, andgreater than or equal to 5 nm. Also desirable, within this range, it isgenerally desirable to have organic electron donors less than or equalto 90, less than or equal to 75, and less than or equal to 60 nm.

The protective shells usually render the organic electron donors solubleor dispersible in a selection of suitable solvents. The thickness of theprotective shell depends on the particular moiety as well as on thesolvents and solutes in the solution. The protective shells for organicelectron donors are about 1 to about 10 nm in thickness. Within thisrange, it is generally desirable to have a protective shell of greaterthan or equal to 1.5, and greater than or equal to 2 nm. Also desirable,within this range, it is generally desirable to a protective shell ofless than or equal to 9, less than or equal to 8, and less than or equalto 6 nm.

Examples of inorganic electron donors include, but are not limited tometal-halide salts, such as titanium tetrabromide (TiBr₄), zirconiumtetrabromide (ZrBr₄), vanadium tribromide (VBr₃), niobium tetrachloride(NbCl₄) or manganese dibromide (MnBr₂) reduced by potassiumtriethylbotohydride (K⁺BEt₃H⁻) or tetraalkylammoniumtriethylborohydride(NR₄ ⁺BEt₃H⁻) (wherein R is an alkyl having 6 to 20carbon atoms) in tetrahydrofuran (THF) for 3 to 6 hours to yield metalclusters stabilized by THF molecules.

Tetrahydrothiophene may also be used in place of THF to stabilizemanganese (Mn), palladium (Pd) and platinum (Pt) containing electrondonors. These inorganic electron donors are made by reducing the metalsalts such as manganese bromide (MnBr₂), platinum chloride (PtCl₂) andpalladium chloride (PdCl₂) with potassium triethylvborohydride(K⁺BEt₃H⁻) or tetraalkylammonium borohydride (NR₄ ⁺BEt₃H⁻) (wherein R isan alkyl having 6 to 20 carbon atoms) in the presence oftetrahydrothiophene.

In one embodiment, inorganic electron donors are derived from the halidesalts or halide complexes of transition metals such as iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium(Pd), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir), platinum(Pt) and gold (Au) by reduction with K⁺BEt₃H⁻ or NR₄ ⁺BEt₃H⁻ (wherein Ris an alkyl having 6 to 20 car These nanoparticles are stabilized byusing quaternary ammonium salts of the formula

wherein R, R′, R″, R′″ may be the same or different and are hydrogen, analkyl having 6 to 20 carbon atoms, an aryl having 6 to 20 carbon atoms,an arylalkyl having 6 to 20 carbon atoms. Betaine surfactants may alsobe used as stabilizers.

In another embodiment, inorganic electron donors are derived fromtransition metals such as Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Ptand Au by stabilizing their halide salts, halide complexes or theiracetylacetonate (acac) complexes using carboxylate salts of the typeNR4⁺R′COO⁻, wherein R is an alkyl having 6 to 20 carbon atoms, and R′ ishydrogen, an alkyl, an aryl or an arylalkyl having 6 to 20 carbon atoms.In yet another embodiment, mixed metal inorganic electron donors may beobtained from mixtures of transition metal halide salts, their halidecomplexes and their acac complexes. In yet another embodiment,electrochemical reduction of the halide salts, halide complexes or theacac complexes of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt and Auare also used to prepare inorganic electron donors using a variety ofstabilizers such as THF, tetrahydrothiophene, quaternary ammonium saltsand betaine surfactants.

The inorganic electron donors generally have particle sizes of 1 to 100nm. Within this range, it is generally desirable to have inorganicelectron donors greater than or equal to 1.5, greater than or equal to 2nm. Also desirable, within this range, it is generally desirable to haveorganic electron donors less than or equal to 50, less than or equal to25, and less than or equal to 15 nm.

Without being limited by theory, the choice of stabilizer has an effecton the electrical properties of the device because different stabilizersexhibit different dielectric constants. The dielectric constant of thestabilizing material surrounding the metal influences the selfcapacitance of the nanoparticles in the matrix material. For example,the self-capacitance of a naked conducting sphere in a dielectric matrixwith dielectric constant κ isC_(sphere)=4πε₀κγwhere r is the radius of the sphere and ε₀ is the permittivity of freespace. On the other hand, the self-capacitance of a conducting spherewith a stabilizer coating having dielectric permittivity, ε_(c), in amatrix with dielectric permittivity ε_(m), * and a relative permittivityε_(r)=ε_(m)/ε_(c) is

$C_{{coated}\text{-}{sphere}} = \frac{4\pi\; ɛ_{m}ɛ_{r}{ab}}{b - {a\left( {1 - ɛ_{r}} \right)}}$where a is the radius of the metal sphere and b is the radius of themetal sphere plus the coating. This can amount to a 20% to 30%difference in capacitance for particles having a size of less than orequal to 10 nm with protective shells having a thickness of 1 to 2 nmand, for example, dielectric constants of 2 and 5 for the coating andthe matrix, respectively.

The electron donors are generally present in the electric fieldprogrammable film in an amount of 0.05 to 45 wt % based on the totalweight of the film. Within this range it is generally desirable to usean amount of for example, greater than or equal to about 3, greater thanor equal to about 5, and greater than or equal to about 8 wt %, based onthe total weight of the film. Also desirable within this range is anamount of less than or equal to about 40, less than or equal to about30, and less than or equal to about 25 wt %, based on the total weightof the film.

Electron acceptors include, but are not limited to 8-hydroxyquinoline,phenothiazine, 9,10-dimethylanthracene, pentafluoroaniline,phthalocyanine, perfluorophthalicyanine, tetraphenylporphine, copperphthalocyanine, copper perfluorophthalocyanine, coppertetraphenylporphine,2-(9-dicyanomethylene-spiro[5.5]undec-3-ylidene)-malononitrile,4-phenylazo-benzene-1,3-diol, 4-(pyridin-2-ylazo)-benzene-1,3-diol,benzo[1,2,5]thiadiazole-4,7-dicarbonitrile, tetracyanoquinodimethane,quinoline, chlorpromazine, tetraphenylporphine, copper phthalocyanine,copper perfluorophthalocyanine, or the like, or combinations comprisingat least one of the foregoing electron acceptors.

The selection of the optimum electron acceptor is influenced by itselectron affinity. It is possible to use one or more electron acceptorsto minimize threshold voltages while offering improved environmentalstability.

The electron acceptors are generally present in the electric fieldprogrammable film in an amount of 0.05 to 45 wt % based on the totalweight of the film. Within this range it is generally desirable to usean amount of for example, greater than or equal to about 3, greater thanor equal to about 5, and greater than or equal to about 8 wt %, based onthe total weight of the film. Also desirable within this range is anamount of less than or equal to about 40, less than or equal to about30, and less than or equal to about 25 wt %, based on the total weightof the film.

When electron donors and electron acceptors are to be combined in thesame formulation, it is believed that some donors and acceptors willreact to form donor-acceptor complexes or, alternatively,charge-transfer salts. The extent of reaction depends on the electronaffinity of the electron donor, the ionization potential of theacceptor, kinetic factors such as activation energies, activationentropies and activation volumes, and energies attributable to matrixeffects. In addition to forming spontaneously as a result of a reactionbetween electron donors and electron acceptors, donor-acceptor complexescan be optionally added to the formulation to adjust “on” and “off”threshold voltages, “on” state currents, “off” state currents and thelike.

A wide array of donor-acceptor complexes may be used. Such complexesinclude, but are not limited to,tetrathiafulvalene-tetracyanoquinodimethane;hexamethylenetetrathiafulvalene-tetracyanoquinodimethane;tetraselenafulvalene-tetracyanoquinodimethane;hexamethylenetetraselenafulvalene-tetracyanoquinodimethane;methylcarbazole-tetracyanoquinodimethane;tetramethyltetraselenofulvalene-tetracyanoquinodimethane; metalnanoparticle-tetracyanoquinodimethane complexes comprising gold, copper,silver or iron, ferrocene-tetracyanoquinoditnethane complexes;tetrathiotetracene, tetramethyl-p-phenylenediamine, orhexamethylbenzene-tetracyanoquinodimethane complexes;tetrathiafulvalene, hexamethylenetetrathiafulvalene,tetraselenafulvalene, hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-Buckmins terfullerene C₆₀ complexes;tetrathiafulvalene, hexamethylenetetrathiafulvalene,tetraselenafulvalene, hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-tetracyanobenzene complexes, tetrathiafulvalene,hexamethylenetetrathiafulvalene, tetraselenafulvalene,hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes, tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-tetracyanoethylene complexes; tetrathiafulvalene,hexamethylenetetrathiafulvalene, tetraselenafulvalene,hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes, tetrathiotetracene; tetramethyl-p-phenylenediamine,or hexamethylbenzene-p-chloranil complexes, or combinations comprisingat least one of the foregoing donor-acceptor complexes.

When donor-acceptor complexes are used, they are generally present inthe film in an amount of 0.05 to 5 wt % based on the total weight of thefilm. Within this range, it is generally desirable to use an amount offor example, greater than or equal to about 0.08, greater than or equalto about 0.1, and greater than or equal to about 0.5 wt %, based on thetotal weight of the film. Also desirable within this range is an amountof less than or equal to about 4.5, less than or equal to about 4, andless than or equal to about 3.5 wt %, based on the total weight of thefilm.

The solvent can be any liquid that dissolves the matrix material; theelectron donors; the electron acceptors; and, optionally, and theoptional donor-acceptor complexes. It is generally desirable that thematrix precursor composition or the dielectric matrix material; theelectron donors; the electron acceptors; and, optionally, and theoptional donor-acceptor complexes remain in solution for a sufficientperiod of time to allow casting of the electric field programmable film.Accordingly, solvent systems that provide kinetically stable orthermodynamically stable solutions are suitable. In general, castingsolvents should have a flash point greater than or equal to 36° C. and aboiling point of 120° C. to 300° C.

Suitable solvents include, but are not limited to 1,2-dichloro-benzene,anisole, mixed xylene isomers, o-xylene, p-xylene, m-xylene, diethylcarbonate, propylene carbonate, R¹—CO—R², R¹—COO—R² and R¹—COO—R³—COO—R²wherein R ¹ and R₂ can be the same or different and represent linear,cyclic or branched alkyl alkylene, alkyne, benzyl or aryl moietieshaving 1 to 10 carbon atoms, and R³ is a linear or branched divalentalkylene having 1 to 6 carbon atoms.

In one embodiment, the electric field programmable film composition canoptionally contain a surfactant to form a colloidal suspension, emulsionor microemulsion comprising water or another suitable carrier. Suitablenonionic surfactants include alcohol ethoxylates, alkylphenolethoxylates, and alkylpolyglycosides. It is desirable to use alcoholethoxylates having, for example, 6 to 24 carbon atoms. It is alsodesirable to use alcohol ethoxylates having, for example, 1 to 20ethylene oxide groups. Alkylphenol ethoxylates having 6 to 24 carbonatoms may also be used as surfactants. In one example, alkylphenolethoxylates may be used as surfactants, wherein the alkylphenol moietieshave 8 to 10 carbon atoms and 1 to 100 ethylene oxide groups. Withinthis range, it is exemplary to have 12 to 20 ethylene oxide groups.Alkylpolyglycosides having 6 to 24 carbon atoms may also be used assurfactants. Within this range, it is exemplary to usealkylpolyglycosides with 6 to 20 carbon atoms. It is also exemplary touse alkylpolyglycosides having 1 to 20 glycoside groups with 9 to 20glycoside groups more exemplary. Ethylene oxide—propylene oxide blockcopolymers may also be used as surfactants.

Suitable quaternary ammonium surfactants include compounds having theformula

wherein R, R′, R″ and R′″ are the same or different and may be an alkyl,aryl or aralkyl group having 1 to 24 carbon atoms that can optionallycontain one or more of phosphorus, oxygen sulfur or nitrogenheteroatoms, and wherein X is F, Cl, Br, I or an alkyl sulfate.

Suitable anionic surfactants include alkylbenzene sulfonates having 6 to24 carbon atoms; olefin sulfonates having 6 to 24 carbon atoms; paraffinsulfonates having 6 to 24 carbon atoms; cumene sulfonate; xylenesulfonate; alcohol sulfates having 6 to 24 carbon atoms; and alcoholether sulfates having 6 to 24 carbon atoms with 1 to 20 ethylene oxidegroups.

Suitable amphoteric surfactants include amine oxide compounds having thegeneral formula

where R, R′ and R″ are the same or different and are each an alkyl, arylor aralkyl group having 6 to 24 carbon atoms that can optionally containone or more P, O, S or N heteroatoms. Another class of amphotericsurfactants includes betaine compounds having the formula:

where R, R′ and R″ may be the same or different and are each an alkyl,aryl or aralkyl group having 6 to 24 carbon atoms that can optionallycontain one or more P, O, S or N heteroatoms, and n is 1 to 10.

If the electric field programmable film composition utilized asurfactant, it is generally desirable for the electric fieldprogrammable film composition to contain less than or equal to 10 wt %surfactant, less than or equal to 3 wt % surfactant and less than orequal to 1 wt % surfactant.

In order to form the electric field programmable film, the electricfield programmable film composition is cast onto a substrate and anysolvent present is then removed. For spin-coating, spin speeds of 200rpm to 6000 rpm may be used. Relative solvent evaporation rates areusually referenced to the evaporation rate of n-butyl acetate at 20° C.Desired evaporation rates for casting solvents are 0.05 to 2.0. Thesolvent evaporation rate for example, should be greater than or equal to0.1. The solvent evaporation rate for example, is less than or equal to1.0.

In manufacturing the electric field programmable film from the electricfield programmable film composition, various methods of manufacturingmay be employed. In one embodiment, the electric field programmable filmis cast from a solvent on a suitable substrate by processes such as spincoating, spray coating, ink-jet coating, dip coating, blade coating andslot coating. In another embodiment, the electric field programmablefilm composition can optionally contain be electrodeposited from acolloidal suspension, emulsion or microemulsion comprising water oranother suitable carrier.

Once deposited, the film can be dried using a convection oven, aninfrared oven, a microwave oven, a radiant heater, a hard-contact orproximity hotplate or other suitable heating device at temperatures of10° C. to 250° C. The time of heating is for a period of 15 seconds to 2hours, depending on the drying method used. It is desired that the filmis brought to within 10° C. of the target temperature for at least 10seconds to 5 minutes. Whatever the method of drying, the final solventconcentration in the film is less or equal to about 10 wt %, with lessthan or equal to 5 wt % being exemplary, and less than or equal to 3 wt% being even more exemplary, based on the total weight of the electricfield programmable film.

As stated above, the film may be used in a cross-point array. When thefilm is used in a cross point array, the electrodes may be electricallycoupled to the electric field programmable film. The cross point arraymay advantageously include an electrical coupling element. An electricalcoupling element is a component interposed between the electric fieldprogrammable film or electric field programmable film element. Examplesof electrical coupling elements are a bit line or a word line. Anelectrical coupling element can provide ohmic contact, contact via aconducting plug, capacitive contact, contact via an intervening tunneljunction, contact via an intervening isolation device such as a diode ora transistor or contact via other electrical devices.

A word line is the conductor or semiconductor that selects the desiredbit in a random access memory device. It is also called the select line.When the word line is asserted, the bit can either be read or written.When the device is symmetrical, the designation of “word line” or “bitline” can be arbitrary. A word line array is a plurality of word linesarranged in essentially parallel fashion. A bit line is the conductor orsemiconductor that reads or writes the desired bit in a random accessmemory device. When the word line is asserted, the bit is selected andcan be either read or written. When the device is symmetrical, thedesignation of “word line” or “bit line” can be arbitrary. A bit linearray is a plurality of bit lines arranged in essentially parallelfashion.

The electric field programmable film obtained from the electric fieldprogrammable film composition may be used in electronic memory andswitching devices or data storage devices. These devices may containeither a single film or multiple films. Devices having multiple filmsare generally termed stacked devices. The following figures depict anumber of exemplary embodiments in which the electric field programmablefilm may be used. FIG. 1( b) shows one example of a cross point arrayhaving a single electric field programmable film, 2, coupled to a firstelectrode, 3, a second electrode, 4, a variable program/read voltagesource connected to the first electrode, 5 and a reference or groundconnected to the second electrode, 6. FIG. 2( a) shows a cutaway view ofa cross-point array data storage device with a continuous electric fieldprogrammable film represented by 7, an array of word lines, an exampleof which is 8, an array of bit lines, an example of which is 9 and theelectric field programmable film element 10 formed by the interposingelectric field programmable film 7 at the intersection of word line 8and bit line 9. FIG. 2( b) shows a cutaway view of a cross-point arraydata storage device with a plurality of pixilated electric fieldprogrammable film elements represented by 11. Each electric fieldprogrammable film element is electrically coupled to a word line,exemplified by 12, and a bit line, exemplified by 13. In addition, thereare a plurality of electrical coupling elements, exemplified by 14interposed between the electric field programmable films and the wordlines.

FIG. 3( a) shows a schematic diagram of a cross point array devicecomprising electric field programmable film elements, represented by 16,electrically coupled to an exemplary bit line, 17, and an exemplary wordline, 18, via exemplary connections, 19 and 20, respectively. Also shownin block diagram form are the sensing electronics, 21 and the pollingelectronics, 22. FIG. 3( b) shows a schematic diagram of a cross pointarray device comprising electric field programmable film elements, anexample of which is shown by 23, electrically coupled to an exemplarybit line, 24, and an exemplary word line, 25. The electric fieldprogrammable film elements are electrically coupled to their respectivebit lines, exemplified by the connection at 24, via isolation diodes, anexample of which is shown by 27 and further electrically coupled totheir respective word lines at 28. Also shown in block diagram form arethe polling electronics, 29 and the sensing electronics, 30 used toaddress the individual bits and amplify the signals obtained from them.

FIG. 4 shows a cutaway partially exploded view of a stacked data storagedevice on a substrate, 31, comprising a first device layer, having avertical line array with a plurality of conducting or semiconductingelectrodes, exemplified by 32, and an insulating material having adielectric constant, 33, an electric field programmable film, 34,electrically coupled to the conducting or semiconducting electrodesexemplified by 32 and the conducting or semiconducting electrodes,exemplified by, 35, in a horizontal line array with each electrode beingisolated from its nearest neighbor by an insulating material having adielectric constant, exemplified by 36, a second device layer, separatedfrom the first device layer by a dielectric insulating layer, 37, havinga vertical line array with a plurality of conducting or semiconductingelectrodes, exemplified by 38, and an insulating material having adielectric constant, 39, an electric field programmable film, 40,electrically coupled to the conducting or semiconducting electrodesexemplified by 38 and the conducting or semiconducting electrodes,exemplified by 41, in a horizontal line array with each electrode beingisolated from its nearest neighbor by an insulating material having adielectric constant, exemplified by 42.

In general, the horizontal lines and the vertical lines intersect eachother without direct physical and electrical contact, and wherein ateach prescribed intersection of a horizontal line and a vertical line,the horizontal line is electrically coupled to the first surface of theelectric field programmable film element and the vertical line iselectrically coupled to the second surface of the electric fieldprogrammable film element and wherein said stacked data storage devicecomprises a configuration selected from

-   -   [H P V D]_(n−1) H P V,    -   [V P H D]_(n−1) V P H,    -   [H P V P]_(m) H, and    -   [V P H P]_(m) V,        where n−1 and m represent the number of repeating layers,        n=1-32, m=1-16, H is a horizontal line array, V is a vertical        line array, P is a set of electric field programmable film        elements arrayed in essentially coplanar fashion, and D is a        dielectric insulating layer.

In addition to single layer memory structures described above,multi-layered structures such as those shown in FIGS. 4, 5 and 6 mayalso be constructed. While the figures indicate only a few device layersfor simplicity, a larger number is contemplated in accordance with theappended claims.

FIGS. 4 and 5 show stacked structures separated by a dielectricisolation layer. Such layers form a substantially plane layer-likestructure, making it possible to stack such planar layer-likestructures, thus forming a volumetric memory device. Isolation layers ofthis invention are intended to isolate the various device layers fromone another electrically, capacitively, and, optionally, optically. Inaddition, the material must be capable of being etched so that via holescan be imparted for the purpose of interconnecting the various layers.Inorganic isolation materials such as silicon oxide, formed chemicalvapor deposition from the decomposition of tetraethylorthosilicate(TEOS) or other silicate, silicon nitride, silicon oxynitride, titaniumdioxide, and the like are used for this purpose. In addition, organicand organosilicon isolation materials such as spin-on glass formulationscomprising siloxanes having C₁-C₁₀ alkane substitution, substitutedsilsesquioxanes having C₁-C₂₀ alkyl, aryl or alkylaryl substitution,fluoropolymers comprising tetrafluoroethylene, polyimides, and the like.

Isolation of individual bits along, for example, a word line isaccomplished using contact diode structures of the kind described andshown in FIG. 5. Stacked devices in which electrodes are shared betweendevice layers are exemplified in FIG. 6. These stacked devices aredistinguished in that they do not use isolation layers. Instead, theword-line is shared between adjacent field programmable film layers.

FIG. 5 shows a cutaway partially exploded view of a stacked data storagedevice having a substrate, 43, a first device layer and a second devicelayer. The first device layer comprises a vertical line array havingconducting or semiconducting lines, exemplified by 44, in contact with aconducting or semiconducting material, exemplified by 45, having adifferent work function than 44 thus forming a contact diode, andinsulators having a dielectric constant, exemplified by 47, an electricfield programmable film, 46, and a horizontal line array comprisingconducting or semiconducting lines, exemplified by 48 and insulatorshaving a dielectric constant, exemplified by 49. The diode comprises ananode comprising a metal having a work function between 2.7 and 4.9 eVand a conducting polymer having a work function greater than 4.5 eV.Portions of the bottom surface of 46 are electrically coupled to thelines, 44 via the contact diodes formed by 44 and 45. Portions of thetop surface of 46 are electrically coupled to the lines, 48.

The semiconducting lines generally comprises a material selected fromp-doped silicon, n-doped silicon, p-doped amorphous silicon, n-dopedamorphous silicon, p-doped polycrystalline silicon, n-dopedpolycrystalline silicon, tantalum suicide, titanium silicide, tungstensilicide, vanadium silicide, polyacetylene, polypyrrole, polyaniline,polythiophene, poly(3,4-ethylenedioxythophene), PEDOT-PSS,poly(para-phenylene), poly(pyridine), polyfuran, polyfluorene,polyphenylenevinylene, polyselenophene, poly(peri-naphthalene),polyazulene, polycarbozole, polyindole, polypyrene, poly(p-phenylenesulfide), polyphenylene oxide, polyquinoline, polyacenaphthylenediyl,polyisothianaphthene, polynaphthothiophene,poly(p-hydro-quinone-alt-thiophene) or poly(furan-co-phenylene).

FIG. 5 further shows, in cutaway form, a second device layer, isolatedfrom the first device layer by an isolating film, 50, having adielectric constant. The second device layer comprises a vertical linearray having conducting or semiconducting lines, exemplified by 51, incontact with a conducting or semiconducting material, exemplified by 52,having a different work function than 51 thus forming a contact diode,and insulators having a dielectric constant, exemplified by 54, anelectric field programmable film, 53, and a horizontal line arraycomprising conducting or semiconducting lines, exemplified by 55 andinsulators having a dielectric constant, exemplified by 56. Portions ofthe bottom surface of 53 are electrically coupled to the lines, 51 viathe contact diodes formed by 51 and 52. Portions of the top surface of46 are electrically coupled to the lines, 55. The first and seconddevice layers in FIG. 5 are shown aligned with one another but can beoffset to facilitate interconnection.

In FIG. 6 is provided a partially exploded cutaway view of yet anotherstacked data storage device comprising a substrate, 57, and three devicelayers. The first device layer comprises a vertical line array havingconducting or semiconducting lines, exemplified by 58, in contact with aconducting or semiconducting material exemplified by 59, having adifferent work function than 58 thus forming a contact diode, andinsulators having a dielectric constant, exemplified by 61, an electricfield programmable film, 60, and a horizontal line array comprisingconducting or semiconducting lines, exemplified by 62 and insulatorshaving a dielectric constant, exemplified by 63. Portions of the bottomsurface of 60 are electrically coupled to the Lines, 58 via the contactdiodes formed by 58 and 59. Portions of the top surface of 60 areelectrically coupled to the bottom sides of the lines, 62.

The second device layer in FIG. 6 comprises the same horizontal linearray as the first device layer, having conducting or semiconductinglines, exemplified by 62, and insulators having a dielectric constant,exemplified by 63, an electric field programmable film, 64, and avertical line array comprising conducting or semiconducting lines,exemplified by 66, in contact with a conducting or semiconductingmaterial, exemplified by 65, having a different work function than 66,thus forming a contact diode, and insulators having a dielectricconstant, exemplified by 69. Portions of the bottom surface of 64 areelectrically coupled to the top surfaces of the lines, 62. Portions ofthe top surface of 64 are electrically coupled to the lines, 66 via thecontact diodes formed by 65 and 66. The horizontal line array,comprising the conducting or semiconducting lines, 62 and insulators,63, is shared by the first and second device layers.

The third device layer in FIG. 6 comprises a vertical line array havingconducting or semiconducting lines, exemplified by 66, in contact with aconducting or semiconducting material, exemplified by 67, having adifferent work function than 66 thus forming a contact diode, andinsulators having a dielectric constant, exemplified by 69, an electricfield programmable film, 68, and a horizontal line array comprisingconducting or semiconducting lines, exemplified by 70 and insulatorshaving a dielectric constant, exemplified by 71. Portions of the bottomsurface of 68 are electrically coupled to the lines, 66 via the contactdiodes formed by 66 and 67. The third device layer in FIG. 6 shares theelectrodes exemplified by 66 with the second device layer via 67.Portions of the top surface of 68 are electrically coupled to the bottomsides of the lines, 70.

FIG. 7 provides, in cutaway, contiguous, 7(a), and exploded, 7(b), viewsof a portion of a data storage device in which the memory elements areisolated by junction diodes. A p-type semiconductor, 72, is used as thesubstrate, with a vertical n+ bit line array, exemplified by 73, aplurality of p+ zones doped within each bit line, exemplified by 74, apatterned matrix for isolating the electric field programmable filmelements, 75, electric field programmable film elements, exemplified by76, and conducting or semiconducting word lines, 77, each in contactwith a row of electric field programmable film elements. The p+ regions,74, and the n+ bit lines, 73, form an array of isolation diodes, whichelectrically isolate the intended bits for reading, writing andaddressing.

Addressing an individual bit in a cross-point array such as those inFIGS. 2 and 3 requires isolation of the selected bit from the contiguousbits as well as the bits along the same word line. In general, thisisolation is effected by introducing an asymmetry in the “on” and “off”threshold voltages for the device where the magnitudes of the “on” and“off” threshold voltages differ significantly.

One method of producing such an asymmetry is by forming a inorganicoxide on one of the electrodes prior to the deposition of the electricfield programmable film. This can be accomplished by allowing the metalof the electrode to form a native oxide in air or, more actively, byoxidizing the metal electrode in ozone. In this way, the two electrodesurfaces are electrically coupled to the electric field programmablefilm in different ways; one is electrically coupled via capacitivecoupling while the other is in direct contact. The oxide coating on theelectrode must be sufficiently thin to enable charge injection into theelectric field programmable film via tunneling, hot carrier injection orelectron hopping. For example, aluminum oxide, thicknesses of 0.5 to 3.0nm are used.

Another method of producing such an asymmetry is by using metals withdiffering work functions. The work function is defined as that energyrequired to remove an electron from the surface of the metal toinfinity. While different crystal faces of metals and other elementsexhibit different work functions, the electrodes used on the electricfield programmable films are polycrystalline. Accordingly, the workfunction comprises an average of the crystalline forms in contact withthe electric field programmable film. By way of example, consider anelectric field programmable film in contact with an aluminum electrodeon one side (Φ˜4.2 electron-volts (eV)) and a nickel electrode on theother (Φ˜5.2 eV). If the forward bias is defined as proceeding from thealuminum electrode to the nickel electrode, with the aluminum electrodebeing the anode, the magnitude of the forward bias voltage required toinitiate the “on” state will be higher than the magnitude of the reversebias voltage required to impose the “off” state. Among the transitionelements, Al, Cr, Fe, Re, Ru, Ta, Ti), V, W and Zr all exhibit workfunctions less than 5 eV, Rh exhibits a work function of approximately 5eV and Au, Cu, Ir, Ni, Pd, and Pt exhibit work functions greater than 5eV.

Still another way to impose asymmetry on devices comprising fieldprogrammable films is to introduce contact diodes using organicconductors and semiconductors. Such diodes are described in L. S. Romanand O. Inganäs, Synthetic Metals, 125, (2002), 419 and can be furtherunderstood by making reference to FIGS. 2( b) and 5. In brief, thesediodes comprise a low work function conducting polymer such aspoly(3-(2′-methoxy-5′-octylphenyl)thiophene) (POMeOPT) (Φ˜3 eV) incontact on one side with an Al electrode (Φ˜4.2 eV) and on the otherside with poly(3,4-ethylenedioxythiophene) doped withpoly(4-styrenesulfonate) (PEDOT-PSS) (Φ˜5.2 eV), which, in turn, is incontact with an aluminum electrode. In the device POMeOPT is interposedbetween the electric field programmable film and the metal electrode.Aluminum or some other metal having a similar work function electrodesuch as copper <110>(Φ˜4.5 eV) is applied to the opposite side of theelectric field programmable film. Other organic conductors andsemiconductors that are used in this invention are doped polyaniline,doped polypyrrole, polythiophene, and polyphenylene vinylene. Inaddition, one can use indium-tin-oxide (ITO) to introduce an asymmetryin the “on” and “off” voltages in like manner to the above examples.

Still another way to introduce an asymmetry in the “on” and “off”voltages is to place the device in contact with a semiconductor diode ofthe kind shown in FIG. 7. Yet another way to isolate the “on” and “off”voltages is to place the device in electrical contact with a fieldeffect isolation transistor. This can be effected such that the fieldprogrammable film is electrically coupled to the source or the drain ofthe transistor either via a metal “plug” electrode or directly, suchthat the device can only be probed or programmed when the gate in an“open” condition.

Some embodiments of the invention will now be described in detail in thefollowing Examples. In the formulation examples all weight percents arebased on the total weight of the electric field programmable filmcomposition unless otherwise expressed.

EXAMPLE 1

Gold nanoparticles were synthesized at room temperature using atwo-phase arrested growth method detailed by M. J. Hostetler, et. al.,Langmuir, 14 (1998) 17). 50 milliliter (ml) aqueous solution of 0.62grams (g) HAuCl4.3H2O (2 equiv) was added into 80 ml toluene solution of3.0 g of tetraoctylammonium bromide (5 equiv). The mixture wasvigorously stirred for 1 hour. The organic phase was collected and 0.4ml dodecanethiol was added to the reaction mixture. The resultingsolution was stirred for 10 minutes (min) at room temperature. Thesolution was then stirred vigorously and 50 ml aqueous solution of NaBH4(0.76 g, 20 equiv) was added over a period of 15 min. The mixture wasfurther stirred at room temperature for 1 hour (h). The organic phasewas then collected, and the gold nanoparticles were precipitated byadding 400 ml methanol. The black precipitate was separated from thesolution. 20 ml tetrahydrofuran was used to dissolve the blackprecipitate and another 200 ml methanol to re-precipitate the goldnanoparticles. This dissolving (in tetrahydrofuran) and precipitating(with methanol) process was repeated three times to remove thephase-transfer catalyst, excess thiol, and by-products. The metalnanoparticles were dried in air or in vacuo.

EXAMPLE 2

Gold nanoparticles were prepared by the same process as Example 1 exceptthat 0.6 ml dodecanethiol was added during the chemical reaction.

EXAMPLE 3

Gold nanoparticles were prepared by the same process as Example 1 exceptthat 0.8 ml dodecanethiol was added during the chemical reaction.

EXAMPLE 4

Silver nanoparticles were synthesized at room temperature using atwo-phase arrested growth method detailed by B. A. Korgel, S. Fullam, S.Connolly, and D. Fitzmaurice, J. Phys. Chem. B, 102 (1998) 8379. 30 mlaqueous solution of silver nitrate (0.31 g) was added into 140 mltoluene solution of phase transfer catalyst (3.2 grams (C8H17)4NBr) andstirred vigorously for 1 hour. The organic phase was subsequentlycollected and 0.4 ml dodecanethiol was added. After thedodecanethiol/Ag+ solution was stirred for 15 min, 90 ml of an aqueoussolution of sodium borohydride (0.85 g NaBH4) solution was addeddropwise over 20 minutes. The reaction mixture was stirred for 12 hoursbefore the organic/nanocrystal-rich phase was collected. 400 ml methanolwas added into the organic phase to precipitate the silver nanoparticlesand the silver nanoparticles were washed with methanol three times. Thesilver nanoparticles were dried in vacuum and stored in nitrogenatmosphere to avoid oxidation by oxygen in air.

EXAMPLE 5

The bottom Al electrodes with the width of 0.2 millimeter (mm) and thethickness of 50 nm were deposited on glass substrates by thermalevaporation. The electric field programmable film was formed byspin-coating 1,2-dichlorobenzene (DCB) solution of 1.2% polystyrene (PS)(as matrix), 0.4% dodecanethiol-protected Au nanoparticles (Au NP byExample 1) and 0.4% 8-hydroxyquinoline (8HQ) (as electron acceptor). Thefilm was then baked at 80° C. for 30 minutes. The device was completedby thermally depositing the top Al electrodes of 50 nm thickness and 0.2mm width at a vacuum of 1×10⁻⁵ Torr. The junction area of the top andbottom electrodes was 0.2×0.2 mm². Such devices are represented by thenomenclature “Al/PS+Au NP+8HQ/Al”. The I-V curve was tested in air usingan HP 4155B semiconductor parameter analyzer. The device exhibited verylow current (1.7 nano ampere (nA) at 1.5V) during the first scan belowthe electrical “on” threshold. A transition took place at approximately3V. The current jumped more than three orders of magnitude. The devicewas stable at the high conductivity state (curve b) with a current of2.2 microamperes (μA) at 1.5V (“on” state). The device was returned tothe OFF state by applying a negative voltage (−2.5V). It was determinedthat the device could return to the “ON” state again under positive biasabove approximately 3V. Hence, the device was stable in both the ON andOFF states and can be switched between these two states by simplyapplying electrical bias.

EXAMPLES 6-13

The devices in example 6 to 13 were fabricated by a process similar tothat in example 5 with different materials as the electrode, matrix,nanoparticles and electron acceptors. The solution for the electricfield programmable film contained 1.2% polymer, 0.4% nanoparticle and0.4% electron acceptor in 1,2-dichlorobenzene. The materials andselected performance parameters were listed in the following Tables 2, 3and 4. (Vth: the threshold voltage at which the “on” transition takesplace, I_(OFF) and I_(ON) are the currents in the low and highconductivity states, respectively).

TABLE 2 Example 6 7 8 Electrode 1 Al Al Al Matrix PS PS PS NanoparticlesExample 4 Example 3 Example 2 Electron acceptor 8HQ 8HQ 9,10-dimethyl-anthracene Electrode 2 Al Al Al V_(th) (V) 3.0 2.7 6.1 I_(OFF) @1/2V_(th) (nA) 1.73 0.4 0.5 I_(ON) @1/2 V_(th) (nA) 23,230 1,000 1,728

TABLE 3 Example 9 10 11 Electrode 1 Al Al Al Matrix PS PS PSNanoparticles Example 2 Example 2 Example 2 Electron acceptorPentafluoro- 29H,31H- Copper (II) aniline phthalocyanine phthalocyanineElectrode2 Al Al Al V_(th) (V) 6.9 4.6 5.3 I_(OFF) @1/2 V_(th) (nA) 0.71.1 1.6 I_(ON) @1/2 V_(th) (nA) 1,075 1,728 2,334

TABLE 4 Example 12 13 Electrode 1 Al Al Matrix PMMA PMMA NanoparticleExample 1 Example 4 Electron acceptor 8HQ 8HQ Electrode 2 Al Al V_(th)(V) 2.4 1.8 I_(OFF) @1/2 V_(th) (nA) 0.3 0.08 I_(ON) @1/2 V_(th) (nA)2,800 26,850

EXAMPLE 14

Substrates comprising indium tin oxide (ITO) on glass were patternedlithographically. The width of the patterned ITO electrodes was 0.2 mm.The electric field programmable film is formed by spin-coating1,2-dichlorobenzene solution containing 1.6% PS, 0.6% 8HQ and 0.45% AuNPs (from Example 2) on patterned ITO on glass substrates. The filmswere baked at 80° C. for 30 minutes. The top Al electrodes of 0.2 mmwidth were deposited at a vacuum of 10⁻⁵ Torr. Electrical bistablebehavior was obtained with a threshold voltage at 2.0 V, an OFF currentof 55 nA at 1.0 V and an ON current of 3,900 nanoamperes (nA) at 1.0V.

EXAMPLES 15-21

Devices in Examples 15-21 were fabricated by the same process as Example5. The results are shown in Table 5. The substrate is glass, the top andbottom electrodes were manufactured from Al having a 0.2 mm width. Thesolution for the electric field programmable film was 1.2% PS, Au NP(from Example 1) of various concentrations and 8HQ of variousconcentrations.

TABLE 5 Example 15 16 17 18 19 20 21 Concentration of Au NP 0.01 0.1 0.51 0.3 0.3 0.3 (%) Concentration of 8HQ (%) 0.4 0.4 0.4 0.4 0.12 0.6 1.2V_(th) (V) 3.1 2.5 2.5 2.4 3 2.5 2.6 I_(OFF) @1/2 V_(th) (nA) 0.46 0.360.46 0.55 8.6 0.46 22 I_(ON) @1/2 V_(th) (nA) 6,700 5,200 3,600 2,000820 4,500 4,200

EXAMPLE 22

Devices were fabricated by the same process as in Example 5. Theformulation for producing the electric field programmable film contained1.2% PS and 0.4% 8HQ in 1,2-dichlorobenzene without Au NP. An electricaltransition takes place at 2.1V. The current is 0.68 and 8,300 nA at 1.0Vin the OFF and ON states, respectively. The device in the ON state couldnot be turned to the OFF state by applying a negative bias

EXAMPLE 23

An I-V curve of the device of example 5 was tested under a vacuum of10⁻³ Torr. The OFF current at half threshold voltage was 3.5×10⁻³ nA,the ON current at half threshold voltage was 3.5×10⁻³ nA.

EXAMPLE 24

The I-V curve of the device of example 5 was tested in nitrogenatmosphere (glove box filled with nitrogen). The OFF current at halfthreshold was 0.1 nA, and the ON current at half threshold was 1,000 nA.

EXAMPLE 25

The device of Example 13 was operated by the following procedures. (1) Apulse of 0.9 V was applied to the device at the OFF state to obtain acurrent of 0.1 nA (this can be defined as “off”); (2) A pulse of 2.5 Vwith a pulse width of 1 μs was applied; (3) A pulse of 0.9 V was appliedto the device obtaining a current of 2,700 nA (this can be defined as“on”); (3) A pulse of −0.8 V with a pulse width of 1 μs was applied tothe device; (5) A pulse of 0.9V was applied to obtain a current of 0.1nA (“off”).

EXAMPLE 26

The device of Example 8 was operated according to the followingprocedures. (1) A pulse of 3.0 V was applied to the device at the “off”state and a current of 0.5 nA was obtained; (2) A pulse of 6.5 V with apulse width of 1 μs was applied; (3) Aa pulse of 3.0 V was applied tothe device and a current of 1,730 nA was obtained (this can be definedas “on”); (3) Aa pulse of −4.0 V with a pulse width of 1 μs was appliedto the device; (5) Aa pulse of 3.0 V was applied to the device to obtaina current of 0.5 nA (“off”).

EXAMPLE 27

A voltage pulse of 5 V with the width of 50 ns was applied to thedevices of example 7 in the “off” state. After applying the pulse, thedevice turned to the “on” state.

EXAMPLE 28

Al electrodes were formed on a glass substrate by thermal evaporation asbefore. A PEDOT-PSS (available from Bayer) coating of about 30 nm wasthen spin coated on Al/glass. The electric field programmable film wasformed by spin-coating a solution of 1,2-dichlorobenzene of 1.2% PS,0.4% Au NPs (from Example 2) and 0.4% 8HQ. A top Al electrode was thenformed by thermal evaporation. The device had stability at the ON andOFF state and the I-V curve was unsymmetrical in the positive andnegative bias.

In FIG. 8 are provided plots of current vs. applied voltage for thedevice of FIG. 1( b), wherein an electric field programmable film ofapproximately 100 nm thickness was spin-cast from a solution comprising0.4 wt % gold nanoparticle electron donor, 0.4 wt %9,10-dimethylanthracene electron acceptor, 1.2 wt % polystyrene matrixmaterial and 98 wt % 1,2-dichlorobenzene solvent, wherein the weightpercents were based on the total weight of the electric fieldprogrammable film composition. After coating, the film and substratewere baked at 80° C. for 30 minutes on a hotplate. The first and secondelectrodes contained evaporated aluminum cross point electrodes having awidth of 0.2 mm, configured so that the electric field programmable filmwas positioned between the electrodes. The programmed voltage source andcurrent measurements were provided by an Agilent 4145B semiconductorparameter tester. A first forward voltage scan, 78, from 0 to 8 V wasperformed, indicating a first current transition from “off” to “on” atapproximately 6.2 V. A second voltage scan from 0 to 8 V, 79, showed a“high” current condition from 0 to 6.2 V, in distinction to the lowcurrent condition observed in the previous plot, 78. During a thirdvoltage scan from 0 to −4 V, 80, a second current transition was inducedfrom “on” to “off” at approximately −3 V.

1. A composition for the formation of an electric field programmablefilm, the composition comprising a matrix precursor composition or adielectric matrix material, wherein the dielectric matrix materialcomprises an organic polymer and/or a inorganic oxide; and an electrondonor and an electron acceptor of a type and in an amount effective toprovide electric field programming.
 2. The composition of claim 1,wherein the matrix precursor composition comprises styrene,4-hydroxystyrene, C₁-C₁₀ linear, branched or cyclic alkyl, C₁-C₁₀linear, branched, or cyclic alkoxy, C₆-C₁₀ aryl or aralkyl, or C₆-C₁₀aryloxy or aralkyloxy substituted styrene, vinyl acetate, vinyl alcohol,(meth)acrylonitrile, (meth)acrylic acid, C₁-C₁₀ linear, branched orcyclic alkyl or C₆-C₁₀ aryl or aralkyl (meth)acrylate esters, C₁-C₁₀linear, branched or cyclic alkyl or C₆-C₁₀ aryl or aralkyl cyanoacrylateesters, C₁-C₁₀ linear, branched, or cyclic alkoxy, C₆-C₁₀ aryl,arylalkyl, aryloxy or arylalkyloxy dialcohols; C₁-C₁₀ linear, branched,cyclic alkoxy, C₆-C₁₀ aryl, arylalkyl, aryloxy or arylalkyloxy diacids,C₁-C₁₀ linear, branched, or cyclic alkoxy; C₁-C₁₀ aryl, arylalkyl,aryloxy or arylalkyloxy dialcohols; C₁-C₁₀ linear, branched, or cyclicalkoxy, C₆-C₁₀ aryl, arylalkyl, aryloxy or arylalkyloxy diacids, C₁-C₁₀linear, branched, or cyclic alkoxy, C₆-C₁₀ aryl, arylalkyl, aryloxy orarylalkyloxy diamines, polyinerizable oligomers comprising at least oneof the foregoing monomers, polymerizable polymers comprising at leastone of the foregoing monomers, or a combination comprising at least oneof the foregoing monomers, oligomers, or polymers, and further whereinpolymerization of the matrix precursor composition provides a dielectricmatrix material.
 3. The composition of claim 1 or 2 wherein thedielectric matrix material is a homopolymer or copolymer and has adielectric constant of greater than
 2. 4. The composition of claim 1 or2 wherein the dielectric matrix material is a homopolymer or copolymerand has a dielectric constant of 2 to
 500. 5. The composition of claim1, wherein the organic polymer is a polyolefins, poly(meth)acrylates,polyesters, polyamides, novolacs, polysiloxanes, polycarbonates,polyimides, polyacetates, polyalkyds, polyamideimides, polyarylates,polyurethanes, polyarylsulfone, polyethersulfone, polyphenylene sulfide,polyvinyl chloride, polysulfone, polyetherimide,polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidenefluoride, polyvinyl fluoride, polyetherketone, polyether etherketone,polyether ketone ketone or a combination comprising at least one of theforegoing organic polymers.
 6. The composition of claim 1, wherein theinorganic oxide is a composition of the formulaA_(w)B_(x)C_(y)O_(z) where w, x, and y are 0 to 30, and z is 1 to 60; Ais calcium, strontium, or barium, B is bismuth, zirconium, nickel orlead, and C is titanium, niobium zirconium vanadium, or tantalum andwherein stoichiometry of the inorganic oxides is constrained to give,approximate charge neutrality.
 7. The composition of claim 1, whereinthe electron acceptor is 8-hydroxyquinoline, phenothiazine,9,10-dimethylanthracene, pentafluoroaniline, phthalocyanine,perfluorophthalicyanine, tetraphenylporphine, copper phthalocyanine,copper perfluorophthalocyanine, copper tetraphenylporphine,2-(9-dicyanomethylene-spiro[5.5]undec-3-ylidene)-malononitrile,4-phenylazo-benzene-1,3-diol, 4-(pyridin-2-ylazo)-benzene-1,3-diol,benzo[1,2,5]thiadiazole-4,7-dicarbonitrile, tetracyanoquinodimethane,quinoline, chlorpromazine, tetraphenylporphine, or a combinationcomprising at least one of the foregoing electron acceptors.
 8. Thecomposition of claim 1, wherein the electron donor is an organicelectron donor or an inorganic electron donor.
 9. The composition ofclaim 8, wherein the organic electron donors are tetrathiafulvalene,4,4′,5-trimethyltetrathiafulvalene,bis(ethylenedithio)tetrathiafulvalene, p-phenylenediamine,N-ethylcarbazole, tetrathiotetracene, hexamethylbenzene,tetramethyltetraselenofulvalene, or hexamethylenetetraselenofulvalene.10. The composition of claim 8, wherein the inorganic electron donorcomprises metal-halide salts or the acetylacetonate complexes oftransition metals that are reduced by K⁺BEt₃H⁻ or NR4⁺BEt₃H⁻ andstabilized using tetrahydrofuran, tetrahydrothiophene, quaternaryammonium salts or betaine surfactants.
 11. The composition of claims 8,9, or 10, wherein the electron donor has a protective organic orinorganic shell.
 12. The composition of claim 1, further comprisingdonor-acceptor complexes, wherein the donor-acceptor complexes aretetrathiafulvalene-tetracyanoquinodimethane;hexamethylenetetrathiafulvalene-tetracyanoquinodimethane;tetraselenafulvalene-tetracyanoquinodimethane;hexamethylenetetraselenafulvalene-tetracyanoquinodimethane;methylcarbazoletetracyanoquinodimethane;tetramethyltetraselenofulvalene-tetracyanoquinodimethane; metalnanoparticle-tetracyanoquinodimethane complexes comprising gold, copper,silver or iron, ferrocene-tetracyanoquinodimethane complexes;tetrathiotetracene, tetramethyl-p-phenylenediamine, orhexamethylbenzene—tetracyanoquinodimethane complexes;tetrathiafulvalene, hexamethylenetetrathiafulvalene,tetraselenafulvalene, hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-Buckminsterfullerene C₆₀ complexes;tetrathiafulvalene, hexamethylenetetrathiafulvalene,tetraselenafulvalene, hexamethylenetetraselenafulvalene,tetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-tetracyanobenzene complexes; tetrathiafulvalene,hexamethylenetetrathiafulvalene, tetraselenafulvalene,hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,or hexamethylbenzene-tetracyanoethylene complexes; tetrathiafulvalene,hexamethylenetetrathiafulvalene, tetraselenafulvalene,hexamethylenetetraselenafulvalene, ortetramethyltetraselenofulvalene-N-alkylcarbazole(C₁-C₁₀, linear orbranched) complexes; tetrathiotetracene, tetramethyl-p-phenylenediamine,hexamethylbenzene -p-chloranil complexes, or a combination comprising atleast one of the foregoing donor-acceptor complexes.
 13. The compositionof claim 1, further comprising a solvent.
 14. An electric fieldprogrammable film comprises: a dielectric matrix material, wherein thedielectric matrix material comprises an organic polymer and/or ainorganic oxide; an electron donor; and an electron acceptor.
 15. A datastorage device comprising the film of claim
 14. 16. A cross point arraycomprising the film of claim
 14. 17. A method for manufacturing anelectric field programmable film comprising: applying the composition ofclaim 1 to a substrate; and removing the solvent from the appliedcomposition to form a film.
 18. A film manufactured by the method ofclaim 17.